The present invention is concerned with a one-step process for the preparation of poly[3,6-N-substituted carbazole-1,3,4-oxadiazole-2,5-diyl]. More specifically, the present invention involves the one-step polymerization of N-substituted carbazole-3,6-dicarboxylic acid with hydrazine or a hydrazine salt of a non-oxidizing acid in the presence of polyphosphoric acid to provide the desired carbazole-oxadiazole copolymer.
It is known in the art that poly[3,6-N-ethyl carbazole-1,3,4-oxadiazole-2,5-diyl] can be prepared by a multi-step polymerization process. Thus, N. D. Negodyaev and T. P. Sokolova in Chemical Abstracts: 88-74564a (deposited document 1975, VINITI 3390-75) describe a two-step route wherein the first step involves the polymerization of a mixture of N-ethylcarbazole-3,6-dicarboxylic acid chloride and the corresponding dihydrazide to a polyhydrazide. The second step involves a cyclodehydration to the polyoxadiazole. These authors further teach that attempts at a one-step process were unsuccessful.
Poly[3,6-N-substituted carbazole-1,3,4-oxadiazole-2,5-diyl] is a useful precursor for the production of electrically conducting polymers as described in commonly assigned U.S. patent application Ser. No. 664,892, filed concurrently herewith, entitled "Carbazole-Oxadiazole Electroactive Polymers".